• Introduction
  
• Data Assimilation
  
• SSI
  
• Harmonics
• Variables
  
• Example
• Sources

What variables are used?

In the model (the part that moves ahead in time to create a forecast), the variables (not including space and time) are:

• ζ=relative vorticity: this is a measure of how much the wind is spinning: how much vortex motion there is.  A basic test for this is: put a merry-go-round in the wind field. If it starts to turn, there is vorticity in the wind.

                                                             

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• D=wind divergence: this is how much the wind is blowing apart or coming together. 



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• Φ=mass, temperature, pressure and gravity combine in this term: it shows whether the air is in (hydrostatic) equilibrium with the air around it.  If it is not in equilibrium, it will result in atmospheric waves; if it is in equilibrium, the air will remain calm.  This is how SSI avoids the initialization step.



• q=specific humidity: how much water vapor is in the air, in units of mass per volume